Anker keyboard shortcuts for Chrome OS

Hello, I’m using the ultra-thin Anker bluetooth keyboard with a chrome OS computer. Keyboard works great but I can’t figure out how to make some of the chrome OS keyboard shortcut functionality work. Specifically, Control/Shift/F5 is supposed to take a partial screenshot but I can’t make it work… I’ve tried also using the blue “fn” key in the lower left corner of the keyboard, I’ve tried different combinations of control/alt/option/command etc.

Any ideas?

Thank you!